1. Field of the Invention
The present invention relates to an ignition controller for a four-cycle internal combustion engine, and more specifically, to an ignition controller for an internal combustion engine capable of securing a stable combustion by avoiding the fuel adhesion state to the ignition plugs.
2. Description of the Related Art
FIG. 7 is a view of the arrangement showing an ignition controller for a conventional internal combustion engine.
In the drawing, an angle sensor 10 disposed to the crank shaft or the cam shaft (not shown) of the internal combustion engine detects the rotational angle of the internal combustion engine and outputs a crank angle signal SGT showing the reference crank angle of each of cylinders and a cylinder identification signal SGC for identifying each of the cylinders.
Usually, a crank angle sensor (not shown) of the angle sensor 10 for creating the crank angle signal SGT is disposed to a crank shaft and a cylinder identification sensor (not shown) thereof for creating the cylinder identification signal SGC is disposed to a cam shaft.
Various sensors 12 for detecting the operating state of the internal combustion engine include a load sensor 14 for detecting a load Q corresponding to an amount of air sucked by the internal combustion engine.
Further, the various sensors 12 include, for example, a water temperature sensor which detects a cooling water temperature TW as another operating state.
Injectors 16 disposed in correspondence with the respective cylinders of the internal combustion engine inject a predetermined amount of fuel by driving the fuel injection valves of the respective cylinders at predetermined timings.
Each of ignition coils 18 disposed in correspondence with the respective cylinders of the internal combustion engine includes a primary winding 18a and a secondary winding 18b constituting a transformer and imposes an ignition high voltage to the ignition plug 20 of each of the respective cylinders from the secondary winding 18b.
A power transistor 22 connected to the primary winding 18a of each of the ignition coils 18 shuts off a primary current il flowing to the primary winding 18a and generates an increased high voltage from the secondary winding 18b.
An electronic control unit 30 (hereinafter, referred to as an ECU) composed of a microcomputer includes an input interface 32 for fetching the crank angle signal SGT, the cylinder identification signal SGC, the load Q, the cooling water temperature TW and the like, a control/calculation circuit 34 for creating drive signals J and P to the injectors 16 and the ignition coils 18 based on various types of information input through the input interface 32 and an output interface 36 for outputting the respective drive signals J and P.
The control/calculation circuit 34 calculates the respective control timings of the injectors 16 and the ignition coils 18 based on the operating state of the internal combustion engine and outputs the drive signals J and P according to the respective control timings.
The drive signal P to the ignition coils 18 acts as a base current of the power transistors 22 and intermittently turns on the power transistors 22 in the sequence of #1 cylinder.fwdarw.#3 cylinder.fwdarw.#4 cylinder.fwdarw.#2 cylinder and sequentially shuts off the primary current i1 supplied to the respective ignition coils 18.
Next, operation of the ignition controller for the conventional internal combustion engine shown in FIG. 7 will be described with reference to the timing chart of FIG. 8.
In FIG. 8, the crank angle signal SGT is composed of a pulse signal according to the rotation of the crank shaft and the rising edges of respective pulses show a first reference position (reference crank angle) B75.degree. (crank angle 75.degree. this side from TDC) corresponding to the respective cylinders (#1-#4) and the falling edges thereof show a second reference position B5.degree. (crank angle 5.degree. this side from TDC).
The cylinder identification signal SGC is composed of a pulse signal offset in correspondence with particular cylinders (for example, #1 and #4 cylinders) and generates a level (H level or L level) at the respective edges (first and second reference positions) of the crank angle signal SGT in a predetermined sequence to thereby specify the respective cylinders (#1-#4 cylinders).
In the case of FIG. 8, the level of the cylinder identification signal SGC at the first reference position B75.degree. is changed by the rotation of the internal combustion engine such that the H level and the L level are alternately repeated, so that a group of the cylinder which are ignited simultaneously (group ignition) can be identified.
Further, the level of the cylinder identification signal SGC at the second reference position B5.degree. is set to the H level only to a particular cylinder (for example, #1 cylinder), so that the specific cylinder can be identified.
Note, various patterns are observed in the cylinder identification signal SGC and crank angle signal SGT, for example, as shown in FIG. 9. The respective cylinders can be immediately identified from the levels of the cylinder identification signal SGC at a pair of the edges B5.degree. and B75.degree. of the respective pulses of the crank angle signal SGT.
That is, as shown in FIG. 10, when the levels of the cylinder identification signal SGC at the respective reference positions B5.degree. and B75.degree. are "1, 1", "the #1 cylinder" is specified, when the levels are "1, 0", "the #3 cylinder" is specified, when the levels are "0, 1", "the #4 cylinder" is specified and when the levels are "0, 0", "the #2 cylinder" is specified as a corresponding cylinder, respectively.
When the respective cylinders are identified, the control/calculation circuit 34 detects the operating state of the internal combustion engine based on the crank angle signal SGT and the cylinder identification signal SGC from the angle sensor 10, the load Q from the load sensor 14 and other signals detected by the various sensors 12. The circuit also calculates the control parameters (timing at which fuel is injected, ignition timing and the like) of each cylinder using the respective reference positions B75.degree. and B5.degree. as control references.
Therefore, the drive signal J to the injectors 16 and the drive signal P to the power transistors 22 (ignition coils 18) are sequentially created in correspondence to the respective cylinders at an optimum timing corresponding to the operating state of the internal combustion engine.
The power transistors 22 are sequentially turned on by the drive signal P and the primary current i1 supplied to the respective ignition coils 18 are shut off in the sequence of #1 cylinder.fwdarw.#3 cylinder.fwdarw.#4 cylinder.fwdarw.#2 cylinder as shown in FIG. 8.
With this operation, the ignition of the ignition plugs 20 of the respective cylinders is controlled in such a manner that the ignition plugs 20 are sequentially discharged. Usually, the timing at which the primary current i1 is shut off (ignition timing) is set to the vicinity of the second reference position B5.degree., that is, in the vicinity of the upper dead point in a compression stroke.
As described above, the control/calculation circuit 34 controls the injectors 16 and the ignition coils 18 of the respective cylinders at the optimum timing according to the operating state.
However, when the ignition plugs 20 are cooled at the start of the internal combustion engine or when fuel adheres to the ignition plugs 20 in the operating state in which a lot of fuel is injected (so-called, a sooting state), a normal combustible environment cannot be created and combustion is made unstable.
Since no countermeasure is taken in the fuel adhesion state (sooting) for the ignition plugs 20 by the ignition controller for the conventional internal combustion engine as described above, there is a problem that when fuel adheres to the ignition plugs 20, a combustion state is made unstable, by which an exhaust (emission) is deteriorated and rotation is varied.
An object of the present invention is to solve the above problem by providing an ignition controller for an internal combustion engine capable of maintaining a stable combustion state at all times by avoiding the adhesion of fuel to ignition plugs.